Voltage doubler starting circuit for discharge lamp

ABSTRACT

A voltage doubler starting circuit converting the AC voltage impressed on the lamp to a DC voltage of twice the peak AC amplitude which is fed back to the lamp terminals. The circuit includes two diodes and two capacitors arranged in a voltage doubling configuration along with a bleeder resistor, and may, if desired, be built into the lamp base or into the lamp itself in the case of a double envelope lamp. The circuit is used with a ballast of the magnetic type having a series secondary power factor correcting capacitor.

United States Patent William ll. Lake Novelty, Ohio July 15, 1970 Dec. 21, 1971 General Electric Company Inventor Appl. No. Filed Patented Assignee VOLTAGE DOUBLER STARTING CIRCUIT FOR DISCHARGE LAMP 4 Claims, 2 Drawing Figs.

Int.Cl 1101] 7/44, H05b 31/30, H05b 41/231 Field of Search 315/49, 58,

[56] References Cited UNITED STATES PATENTS 2,928,024 3/1960 Dawley..... 315/205 X 3,233,148 2/1966 Lake 315/200 3,275,922 9/1966 Meyer at al 315/200 X Primary Examiner- Roy Lake Assistant ExaminerSiegfried H. Grimm Attorneys-Ernest W. Legree, Henry P. Truesdell, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT: A voltage doubler starting circuit converting the AC voltage impressed on the lamp to a DC voltage of twice the peak AC amplitude which is fed back to the lamp terminals. The circuit includes two diodes and two capacitors arranged in a voltage doubling configuration along with a bleeder resistor, and may, if desired, be built into the lamp base or into the lamp itself in the case of a double envelope lamp. The circuit is used with a ballast of the magnetic type having a series secondary power factor correcting capacitor.

FATENTEU UEUZI 197i 3 zmwm T 0 v Tm mm A M s UQ b VOLTAGE DOUBLER STARTING CIRCUIT FOR DISCHARGE LAMP CROSS REFERENCES TO RELATED APPLICATIONS Copending application Ser. No. 757,l 80, filed July 3 l 1968 by William H. Lake, entitledDischarge Lamp Ballasting, now U.S. Pat. No. 3,527,982, and similarly assigned.

Copending application Ser. No. 54,880 filed July 15, 1970, by William H. Lake and Nicholas W. Medendorp, entitled Resistively Ballasted Discharge Lamp, and similarly assigned.

BACKGROUND OF THE INVENTION The invention relates to a starting circuit for use with lamps having a high starting voltage and which may be built into the lamp itself or its base as an integral part of the lamp or provided as a separate unit.

In recent years some new high-intensity metal vapor discharge lamps have appeared which are difficult to start by comparison with conventional mercury vapor lamps of similar input rating. One such lamp is that covered by U.S. Pat. No. 3,234,42l-Reiling, Metallic Halide Electric Discharge Lamps, which utilizes a quartz arc tube containing mercury and metal halides such as sodium, thallium and indium iodides. Another lamp is that covered by U.S. Pat. No. 3,248,590Schmidt, High Pressure Sodium Vapor Lamp, which discloses a sodium vapor lamp utilizing an envelope of alumina ceramic containing a sodium filling in a new highpressure range. In the metal halide lamp particularly, ti has been a design goal to achieve a lamp which would operate interchangeably with a mercury vapor lamp of the same wattage or rating on the usual mercury vapor lamp ballast. In order to achieve reliable starting of the metal halide lamp, an auxiliary starting electrode has been provided but this solution tends to downgrade maintenance and overall lamp reliability. A bimetal switch was then added to the lamp according to U.S. Pat. No. 3,226,597Green, High Pressure Metal Vapor Discharge Lamp, which connected the starting electrode to the adjacent main electrode after starting of the lamp to eliminate any potential difference between them tending to cause electrolysis. While this solution has been satisfactory, it has increased costs and contributed its own reliability problem.

The object of the invention is to provide an improved system to facilitate the starting of lamps and particularly one which can be added to a metal halide lamp to improve its starting characteristics to the level of the conventional mercury vapor lamp.

SUMMARYOF THE INVENTION In accordance with the invention, a separate starting circuit is provided in the form of a rectifier capacitor network comprising two stages each consisting of a rectifier and a capacitor connected in a voltage-doubling circuit. This circuit causes the AC voltage impressed on the lamp to be converted to a DC voltage having twice the peak amplitude of the applied AC voltage. This DC voltage is fed back to the lamp terminals through a bleeder resistor and builds up to a charge having a magnitude of 2.8 times the open circuit AC voltage generated by the ballast. The charge builds up to this value over a few cycles before the lamp becomes ionized. As soon as the lamp starts, the charge across the first stage voltage doubling capacitor is substantially dissipated and the circuit thereafter draws such a small current from the line that it has no signifi cant effect upon the operation of the lamp.

DESCRIPTION OF DRAWINGS In the drawing wherein like reference characters indicate corresponding elements in the several figures:

FIG. 1 illustrates schematically a lamp starting circuit embodying the invention.

FIG. 2 illustrates somewhat diagrammatically a high pressure metal vapor arc lamp having an integral starting circuit according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT O somewhat diagrammatically to indicate and auxiliary starting circuit built into the base.

Referring to FIG. I, ballast 2, which may be of the kind sometimes known as a constant wattage ballast, comprises a primary winding P which is connected across I 15-120 volt, 60 cycle AC terminals 3,4. The output circuit comprises a secondary winding S connected in series with the primary winding and a secondary power factor correcting capacitor C to output terminals 5,6. The primary and secondary are magnetically coupled together but with substantial leakage reactance between them in order to effect current regulation in the output circuit. The terminal 5,6 would normally be the eyelet and shell terminals of a conventional mogul screw socket (not shown) adapted to accommodate the mogul screw base 7 of a high-intensity metal vapor discharge lamp comprising center contact 5' and screw shell 6' as shown in FIG. 2.

The discharge or arc tube proper indicated L has its terminals 5",6" connected across terminals 5',6, all similarly numbered terminals being electrically coincident. The first stage of the voltage doubling circuit consisting of capacitor C, and diode D, connected in series is shunted across arc tube L with diode D, conducting forwardly from terminal 6. The second stage consisting of diode D, and capacitor C, connected in series is shunted across diode D, of the first stage, with diode D, conducting forwardly from the junction of D, and C,. A bleeder resistor R connects the junction of diode D, and capacitor c, to terminal 5'. It is important that the series power factor correcting capacitor C by much larger (preferably 10 times or more) than capacitor C, in the first stage, and that capacitor C, in the first stage by much larger (preferably 10 times or more) than capacitor C, in the second stage of the voltage doubling circuit. By way of example, in a conventional constant wattage power factor-corrected ballast for a 400-watt mercury lamp, the capacitance of C may be 25 microfarads, that of C, may be 0.5 microfarad, that of C, may be 0.01 microfarad, and the bleeder resistor R may be 40,000 ohms. Since R in series with D, and D, is shunted across the lamp during operation and conduction occurs on one half cycle, R should be large enough to limit the wasted current to a small value.

In the operation of the circuit, the arc tube L may initially be considered as an open circuit. When a voltage is applied across two capacitors in series, the voltage division between them is inversely proportional to the capacitance of each. Thus letting V be the voltage applied across capacitors C and C, in series, the voltage across C will be given by V =VX C,/(C+C,), and the voltage across C, will be VC,=V C/C+C1 In this instance the capacitance of C is 50 times greater than that of C,. Therefore for practical purposes as regards the division of voltage between C and C,, C may be considered a short circuit and the entire voltage considered to be developed across C,. Likewise since C, is 50 times greater than C,, as between C, and C,, C, may be considered a short circuit and the entire voltage considered to be developed across C,.

Considering a half cycle when terminal 6 is positive relative to terminal 5, forward conduction through diode D, will charge capacitor C, substantially to the peak E of the applied voltage with the polarity indicated (neglecting charge on C). On the next half cycle when terminal 5 is positive relative to terminal 6, forward conduction through diode D, will cause capacitorC, to charge with the polarity indicated. The voltage effectively applied is the open circuit voltage plus the charge already stored in capacitor C,. The voltage division between capacitor C, and C, will again be proportional to the inverse of capacitance, So practically the entire-voltage will occur across capacitor C and C will charge to 2E with the polarity indicated.

The voltage developed across capacitor C, is slowly discharged through bleeder resistor R into the power factor correcting capacitor C. The time constant of the discharge of C into C is given by CR and is quite long. This means in effect that capacitor C will take several cycles of the applied AC voltage to charge up to a voltage of approximately 2E. However, before such a voltage is reached, arc tube L will ionize and the lamp will start. After the lamp is started, the voltage doubling circuit is effectively disabled because capacitor C discharges through arc tube L at every half cycle.

In a practical lamp such as represented diagrammatically in FIG. 2, the voltage-doubling starting circuit may be made of an integral part of the lamp. The two diodes D and D, may be grain of wheat size silicon rectifiers sealed in vitreous material and capable of withstanding temperatures of several hundred degrees centigrade. The capacitances C and C, may consist of compact ceramic capacitors using barium titanate for the dielectric which are likewise capable of withstanding high temperatures. The resistor R may consist of a spirally cut thin film on a ceramic tube and is likewise compact and capable of withstanding high temperature. All the components of the voltage-doubling circuit may be mounted either within the outer jacket 8 of the lamp or within the mogul screw shell of the lamp base 7.

The physical arrangement of the components within the base shell may be similar to that described and illustrated in copending application Ser. No. 54,880 filed by myself and Nicholas W. Medendorp on July 15, 1970, entitled Resistively Ballasted Discharge Lamp and assigned to the same assignee as the present invention, which application is hereby incorporated herein by reference.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A discharge lamp for operation on a ballast of the kind which includes a series power factor correcting capacitor comprising:

an arc tube having terminals for connection across said ballast;

a voltage-doubling feedback circuit comprising a first stage including in series a first capacitor and a first diode connected shunt across said are tube;

and a second stage including in series a second diode and a second capacitor connected in shunt across said first diode;

said second diode having forward conduction in the shunt circuit in a direction opposite to the first diode,

said second capacitor being connected to one side of said are tube,

a bleeder resistor connecting the junction of said second diode and second capacitor to the other side of said are tube;

said first capacitor having a capacitance which is smaller than that of the series power factor correcting capacitor; and

said second capacitor having a capacitance which is smaller than that of the first capacitor.

2. A lamp as in claim 1 wherein the capacitance of said first capacitor is not more than one-tenth that of the series power factor correcting capacitor, and that of said second capacitor is not more than one-tenth that of the first capacitor.

3. A lamp as in claim 1 of the double envelope type including an outer jacket surrounding said are tube and wherein said voltage-doubling feedback circuit is an integral part of the lamp.

4. A lamp as in claim 1 of the double envelope type including an outer jacket surrounding said are tube, a screw base mounted on the neck of said outer jacket and wherein elements of said voltage doubling feedback circuit are located within said screw base. 

1. A discharge lamp for operation on a ballast of the kind which includes a series power factor correcting capacitOr comprising: an arc tube having terminals for connection across said ballast; a voltage-doubling feedback circuit comprising a first stage including in series a first capacitor and a first diode connected shunt across said arc tube; and a second stage including in series a second diode and a second capacitor connected in shunt across said first diode; said second diode having forward conduction in the shunt circuit in a direction opposite to the first diode, said second capacitor being connected to one side of said arc tube, a bleeder resistor connecting the junction of said second diode and second capacitor to the other side of said arc tube; said first capacitor having a capacitance which is smaller than that of the series power factor correcting capacitor; and said second capacitor having a capacitance which is smaller than that of the first capacitor.
 2. A lamp as in claim 1 wherein the capacitance of said first capacitor is not more than one-tenth that of the series power factor correcting capacitor, and that of said second capacitor is not more than one-tenth that of the first capacitor.
 3. A lamp as in claim 1 of the double envelope type including an outer jacket surrounding said arc tube and wherein said voltage-doubling feedback circuit is an integral part of the lamp.
 4. A lamp as in claim 1 of the double envelope type including an outer jacket surrounding said arc tube, a screw base mounted on the neck of said outer jacket and wherein elements of said voltage doubling feedback circuit are located within said screw base. 